The effects of erosional and management history on soil organic carbon stores in ephemeral wetlands of hummocky agricultural landscapes

Carbon sequestration by agricultural soils has been widely promoted as a means of mitigating greenhouse gas emissions. In many regions agricultural fields are just one component of a complex landscape matrix and understanding the interactions between agricultural fields and other landscape components such as wetlands is crucial for comprehensive, whole-landscape accounting of soil organic carbon (SOC) change. Our objective was to assess the effects of management and erosional history on SOC storage in wetlands of a typical hummocky agricultural landscape in southern Saskatchewan. Wetlands were classed into three land management groups: native wetlands (i.e., within a native landscape), and uncultivated and cultivated wetlands within an agricultural landscape. Detailed topographic surveys were used to develop a digital elevation model of the sites and landform segmentation algorithms were used to delineate the topographic data into landform elements. SOC density to 45 cm was assessed at seven uncultivated wetlands, seven cultivated wetlands, and twelve native wetlands. Mean SOC density decreased from 175.1 mg ha¿ 1 to 30 cm (equivalent mass depth) for the native wetlands to 168.6 mg ha¿ 1 for the uncultivated wetlands and 87.2 mg ha¿ 1 for the cultivated wetlands in the agricultural field. The SOC density of sediment depositional fans in the uncultivated wetlands is high but the total SOC stored in the fans is low due to their small area. The uncultivated wetlands occupy only 11% of the site but account for approximately 23% of SOC stores. Re-establishing permanent vegetation in the cultivated wetlands could provide maximum C sequestration with minimum energy inputs and a minimum loss of productive acreage but the overall consequences for the gas emissions would have to be carefully assessed